This application relates to copending application Ser. No. 070,973, filed July 7, 1987. The invention relates to temperature changing devices and, in particular, to portable or disposable devices for heating and cooling separate hot and cold portions of food.
In serving food it is preferable to maintain hot foods and cold foods in their respective states until consumption. It would be advantageous for restaurants to be able to provide complete meals, including a hot entree and vegetable and a cold salad, dessert and beverage, and provide means for heating the hot portion and cooling the cold portion.
Similarly, a single food item may comprise hot and cold portions, the temperature of which are preferably maintained until consumption. For example, fast food hamburgers often include, in addition to the bun, meat patty and condiments, various vegetables such as lettuce and tomato. It is deemed advantageous to keep the meat patty hot until consumption. However, prolonged exposure to heat tends to wilt lettuce and tomato, rendering them relatively unpalatable. Thus, it is also deemed advantageous to keep the lettuce and tomatoes cool until consumption. Therefore, to preserve the palatability of such a sandwich, it is logical to keep the components separated as long as possible, preferably until just before eating. On the other hand, because fast food restaurants are high-volume operations, the logic of palatability has traditionally taken a back seat to the expediency of volume. Since the dawn of fast food restaurants, hamburgers have been prepared ahead of time, leaving the meat patty to cool and the lettuce and tomato to heat. As a result, the consumer received a sandwich in which the components had reached a steady-state temperature throughout. The deleterious effects of allowing the meat patty to cool were somewhat overcome in the prior art by placing the entire sandwich in some type of heating device, usually under heat lamps or on a steam table. This method, however, exacerbated the problem of heating the lettuce and tomato.
Recently, one restaurant chain has attempted to overcome this problem with a hamburger sandwich served in a dual package. The package is a foam container, one side of which contains the hot meat on the lower half of the bun, and the other side of which contains the lettuce and tomato on the upper half of the bun. The stated objective of this arrangement is to keep the hot side hot, and the cool side cool.
To a certain extent, this arrangement is successful. Keeping the hot and cool components separate prevents direct heat transfer between the hot meat patty and the cool lettuce and tomato. Nevertheless, both sides of the sandwich come to room temperature within a short period of time. This is due to the relatively poor insulation afforded by the foam containers. Thus, unless such a sandwich is eaten soon after being placed in the container, it will be close to room temperature. This presents a problem for consumers unable to eat their sandwiches at the restaurant. For example, those who wish to eat in their cars, at beaches or at picnic areas must do so with a sandwich which is tepid at best.
One alternative method for maintaining the temperature of separate hot and cold portions of food would be to use containers made of better insulation. For example, the typical fast food package is made of foam, 0.070 inch thick. The insulation quality could be improved at the expense of both cost and space. Apparently, the industry has not found it feasible to improve the insulative quality of its packaging.
Moreover, foam packages are not biodegradable, and their perpetual existence has led legislatures in several states to consider banning their use. These environmental concerns are not the least of the drawbacks of foam containers.
Accordingly, in food serving in general, and fast food serving in particular, there has existed a long-standing need for a relatively small, inexpensive device to maintain the temperature of separate hot and cold portions of food.
The use of two chambers to produce a cooling effect around one chamber is illustrated in U.S. Pat. No. 4,250,720 to Siegel and Great Britain Patent No. 2,095,386 to Cleghorn, et al. These patents disclose a two-chamber apparatus connected by a tube. One chamber contains a refrigerant liquid and the other contains a sorbent. Fluid communication between the two chambers is selectively allowed by a valve in the tube. The Siegel patent uses water as the refrigerant liquid, while the Cleghorn, et al. patent is not limited to water. The Siegel patent envisions the use of such a cooling device to cool food or beverages.
The prior art temperature changers, as exemplified by the Siegel and Cleghorn, et al. patents, contemplate a device for either heating or cooling. In a cooling device, the heat generated by the sorbent is waste heat. Likewise, in a heating device, the refrigeration accomplished by the liquid is wasted.
Furthermore, none of the prior art patents disclose a structure suited for simultaneously heating and cooling separate hot and cold portions of food. Rather, the structures are primarily devoted to the heating or cooling of a single portion See Siegel FIGS. 2-4. Moreover, none of the prior art structures particularly address the problems encountered in using a device which is inexpensive and disposable to heat and cool separate hot and cold portions of food. For example, the prior art envisions use of rigid containers for both the liquid and sorbent. Such rigid containers may be relatively expensive and potentially prohibitive for disposable use in high-volume, low-margin operations such as fast food or other food operations.